Traditionally, machining of metal workpieces to produce desired articles, such as hobbing processes to produce spur and helical gears, shafts, splines, and the like has been performed in the presence of a coolant medium supplied to the point of engagement of a tool and workpiece. Aside from the obvious function of cooling the tool and workpiece, coolant also reduces tool wear and serves to flush metal chips, which emanate from a machined workpiece, away from the area of engagement of tool and workpiece and out of the machine. Once flushed away from the tool and workpiece, chips may be separated from the coolant by filtering or by magnetic separator means as is well known in the art.
While coolant certainly has many advantages, it also has its drawbacks. Coolant is expensive to purchase, and in some cases disposal costs are just as expensive. Coolant mist and coolant oil smoke are considered to be environmental hazards. Therefore, machines must include a mist/smoke collector as a means to remove such airborne contaminants from the atmosphere within the machine enclosure. Coolant circulation in a machine tool requires a pump and hoses to deliver coolant to the machining area, and a chip separator to remove metal chips from the coolant. Such separators are somewhat more complicated than simple powered drag lines used to convey dry chips. In some cases, filters may be needed to remove other debris from the coolant, or a coolant chiller may be required to control both the coolant and the machine equilibrium temperature.
Recently, dry machining processes such as dry hobbing of cylindrical gears and dry cutting of bevel gears have drawn attention as an alternative to processes utilizing coolant (wet machining processes). See, for example, Phillips, "New Innovations in Hobbing--Part II", Gear Technology, November/December 1994, pp. 26-30, and, Stadtfeld, "Gleason POWER-DRY-CUTTlNG.TM. of Bevel and Hypoid Gears", The Gleason Works, Rochester, N.Y., May 1997.
It may be seen that dry machining has the potential to overcome many serious and costly drawbacks associated with the use of a liquid coolant. Also, dry chips are normally more valuable as a recyclable material than chips which are residually wetted by a process fluid. Parts cut without coolant do not need washing, prior to further processing such as heat treatment
However, the heat generated in dry machining processes is a contributor to tool wear and it also may have detrimental effects on the machine itself, causing differential growth of components such as spindles, bearings, or the machine frame. Much of the process heat in dry machining is removed by the chips that must be removed from the machine as quickly as possible and in a manner by which they do not contact the machine frame for any extended period of time.
One way to remove dry chips is to permit the hot chips to slide by gravity toward a chip conveyor built into the base of a hobbing machine. Such a chip removal system is shown in Ophey, "Gear Hobbing Without Coolant", Gear Technology, November/December 1994, pp. 20-24.
Another method of removing chips from a hobbing machine capable of wet and dry hobbing is known from U.S. Pat. No. 5,586,848 to Suwijn wherein the chips are discharged into the machine base where a reversible transfer mechanism carries them to respective wet or dry outlets.